An improved channel estimation for underwater acoustic OFDM and COFDM systems

Abstract

Recently, there has been a tremendous increase in research and development of underwater communication systems. Orthogonal frequency division multiplexing has been widely employed for underwater acoustic communication because of its numerous advantages. Coding as well as interleaving techniques can be used along with orthogonal frequency division multiplexing for improving the error correction capability of the receiver. For demodulating the signal with fairly acceptable accuracies, the channel parameters need to be estimated at the receiver. Channel estimation can be performed by inserting pilots into the sub-carriers of an OFDM symbol. Underwater channels exhibit sparse channel impulse response and hence, the channel can be estimated using the compressive sensing techniques for properly reconstructing the received signals. Dictionary-based sparse channel estimation is presented in this paper which outperforms the channel estimation by LS and MMSE estimations. The results have been compared for various environmental conditions as well as for various numbers of pilots. It has been observed that the number of pilots is to be chosen as a trade-off between channel estimation accuracy and bandwidth efficiency.